1. Field of the Invention
The present invention is related to optical collimators and methods for making them, and more particularly to optical collimators which do not use glue or epoxy to attach components thereof together.
2. Description of the Prior Art
An optical collimator with a Graded Index (GRIN) lens is used for collimating scattered light emitting from an output end of an optical fiber. The collimated light may be efficiently and controllably utilized for transmission or testing.
As shown in FIG. 1, a conventional optical collimator 100 comprises an optical fiber 110, a ceramic ferrule 120, a GRIN lens 130 and an outer glass tube 140. The ferrule 120 has an inner end 122, an outer end 124, and a through hole 126 defined between the inner and outer ends 122, 124. A diameter of the through hole 126 is greater than a diameter of the optical fiber 110. A cone-shaped opening (not labeled) is defined in the outer end 124, in communication with the through hole 126. The optical fiber 110 is typically sealed in the through hole 126 by UV-curved epoxy and 353-ND epoxy. To improve optical performance, the inner end 122 of the ferrule 120 and an inner end 112 of the optical fiber 110 are ground and polished to an oblique angle relative to an imaginary line that is perpendicular to respective longitudinal axes of the ferrule 120 and the optical fiber 110. The angle is typically between 6 and 8 degrees. The GRIN lens 130 has an inner end 132 and an outer end 134. The inner end 132 of the GRIN lens 130 is adjacent the inner end 122 of the ferrule 120, and is obliquely ground and polished to be parallel to the inner end 122 of the ferrule 120. The longitudinal axis of the GRIN lens 130 is aligned with the longitudinal axis of the optical fiber 110. The ferrule 120 and the GRIN lens 130 are positioned and aligned in the glass tube 140, so that output light from the GRIN lens 130 can be accurately focused on the inner end 112 of the optical fiber 110. The ferrule 120 and the GRIN lens 130 are then fixed in place in the glass tube 140 by UV-curved epoxy and 353-ND epoxy.
When the optical fiber 110 is epoxied to the ferrule 120, and when the GRIN lens 130 and the ferrule 120 are epoxied to the glass tube 140, excess epoxy may contaminate the inner ends 112, 132 of the optical fiber 110 and GRIN lens 130. Such contamination reduces the output of the optical fiber 110, and diminishes the performance of the GRIN lens 130. The optical collimator 100 is prone to have large insertion loss. In addition, such contamination is difficult to remove. Furthermore, it is difficult to readjust the relative positions of the optical fiber 110 and the GRIN lens 130 after they have been secured in position. Moreover, typical epoxies need baking to be cured. Common epoxies have a coefficient of thermal expansion several times larger than that of the GRIN lens 130. During baking of the epoxy, the accurate relative positions of the optical fiber 110 and the GRIN lens 130 are frequently altered. Accurate focusing of light from the optical fiber 110 to the GRIN lens 130 is accordingly diminished.
An improved optical collimator is needed to overcome the above-described numerous disadvantages of conventional optical collimators.
Accordingly, an object of the present invention is to provide an inexpensive optical collimator having low insertion loss.
Another object of the present invention is to provide an optical collimator that eliminates the risk of contamination caused by epoxy or glue.
A further object of the present invention is to provide an optical collimator that allows easy readjustment of positions of a Graded Index (GRIN) lens and an optical fiber therein.
To solve achieve the objects set out above, an optical collimator in accordance with a preferred embodiment of the present invention comprises an optical fiber, a metal ferrule, a GRIN lens and an outer metal tube. The optical fiber has an exposed end which is coated with metal. The exposed end of the optical fiber is inserted into the ferrule and laser welded thereto. The GRIN lens is also coated with metal. A plurality of soldering holes is defined in a periphery of the outer tube. Solder is applied to the ferrule and the GRIN lens through the holes to firmly connect the outer tube, the ferrule and the GRIN lens together. After assembly, if the position of the GRIN lens or the optical fiber is found to be inaccurate, the GRIN lens and the ferrule can be easily resoldered.
Other objects, advantages and novel features of the present invention will be apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings, in which: